338 



DESIGN IN NATURE 



acting at first hand. Tlie streaming is spontaneous and voluntary, and lias no connection with contraction or 

 elasticity, with irritabihty or extraneous stimulation, or with reflexes of any kind. The centrifugal, streaming, 

 radiating, pseudopodic movements, with their concomitant centripetal, retiring, or returning movements, are never 

 haphazard or accidental. They are, in the strictest sense of the term, voluntary, co-ordinated, purpose-like move- 

 ments ; the object of the double movement being to secure food and convey it into the interior of the body. 



As showing common ground between force, growth, and structure, examples are numerous among the Foraminifera 

 and allied groups, where spines and hard permanent substances are developed and arranged in a manner altogether 

 resembling the distribution and arrangement of the soft, streaming, thread-Uke pseudopodia described. In such 

 cases a symmetrical appearance results. In certain instances an internal skeleton makes its appearance, and when 

 it does, it, for the most part, assumes a concentric, radiating, symmetrical arrangement frequently met with in crystals, 

 plants, and various parts of the higher animals. 



The concentric, radiating arrangement referred to is seen in the Radiolaria, the characteristic feature of which 

 is the presence of a membranous " central capsule " which divides the body into two zones, an intra-capsula zone 



including the nucleus, and an extra-capsula zone from 

 which the pseudopodia and spines radiate (Figs. 71 

 and 72). 



The body of the Foraminifera consists generally of 

 a transparent sarcode or protoplasm ; the sarcode being 

 occasionally of a brown, pink, or violet tint. The 

 animal is for the most part divided into segments or 

 compartments by septa or divisions in the shell ; the 

 sarcode of each compartment being united by slender 

 threads (stolons) of that material. The continuitv of 

 the substance of the animal is thus secured. 



The Foraminifera, Uke other Protozoa, possess a 



nucleus with, in some cases, nucleoli. They also, in not 



a few cases, possess contractile vacuoles. The nucleus 



and nucleoli which are immediately connected with 



reproduction are frequently covered with fine strands 



of chromatin. The nucleus sometimes divides by binary 



fission, at other times the nucleoli form a morula-like centre inside the nucleus, the protoplasm outside the 



nucleus invading it and breaking it up into globules ; on other occasions, as shown by Lister in the nucleus of 



Polystomella crispa, a karyokinetic division of the nucleus takes place similar to what is seen at Fig. 73. 



In this figure (73) the radiating arrangement of parts is seen to great advantage, and one cannot help feehng 

 that the lines of force and of growth are in this, as in many other cases, more or less identical. 



The Protozoa, of which gromia, paramecium, and amoeba are examples, have been conveniently divided by Messrs. 

 Parker and Haswell ^ into five classes, which I take the hberty of quoting, the more especially as each class is accom- 

 panied by a useful definition : — 



" Class 1. — Rhizopoda. Protozoa in which the amoeboid form is predominant, the animal always forming 

 pseudopods. Flagella are often present in the young, and occasionally in the adult. Encystation frequently occurs. 

 " Class 2.—Mycetozoa. Terrestrial Protozoa in which the plasmodial phase is specially characteristic, as is also 

 the formation of large and often complex cysts. 



" Class 3.—Mastigophora. Protozoa in which the flagellate form is predominant, although the amoeboid and 

 encysted conditions frequently occur. 



" Class i.—Sporozoa. Parasitic Protozoa without organs of locomotion in the adult. Encystation is almost 

 universal, and in the young may be flagellate or amoeboid. 



" Class ^.—Infusoria. Protozoa which are always ciliated, either throughout life or in the young condition." 

 The five classes enumerated introduce us to some important distinctions which will be very useful in dealing 

 with other rudimentary forms now to be considered. 



Fio. 73. — Karyokinetic division of the nucleus in Aeantlwcystis (after 

 Schaudinn). 



§ 63. The Mycetozoa. 



Perhaps the lowest animal form— if as animal it can be regarded— is supphed by the Mycetozoa. This I 

 have figured and described at length at section 57, Fig. .59, p. 302. It may suffice to say here that it occupies 



' " A Text-book of Zoology," vol. i. pp. 43, 44. Macmillan, 1897. 



